The main goal of the research remains the development of more efficient methods of ECG computer analysis. A large data base derived from eight hospitals has been accumulated and continues to be enlarged. This extension data base enabled us to test many complex statatistical procedures for their efficiency in ECG diagnosis. The computer program which is routinely used at present leads to quantitative probability statements for each diagnostic entity under consideration. The system was recently subjected to a field trial by transmitting daily orthogonal ECG's from a hospital in Massachusetts to the computer center in Washington, D.C. Results of the computer analysis were transmitted back to the hospital by teletypewriter. They were compared with conventional 12-lead ECG interpretations performed by two experienced electrocardiographers. In 1,191 cases out of 3,782, it was possible to arrive at a definite clinical diagnosis on the basis of independent information, i.e., without using ECG information. Only these documented cases were used in the comparison. A correct computer diagnosis could be obtained in 88 percent of the series. The conventional 12-lead ECG analysis resulted in 64 percent correct interpretations with an additional 8 percent of partially correct interpretations and 28 percent misclassifications. Thus, computer analysis led to an increase in correct diagnostic classifications by more than 20 percent, mainly through use of multivariate statistical techniques.